4,731 research outputs found
Describing gluons at zero and finite temperature
Any description of gluons requires a well-defined gauge. This is complicated
non-perturbatively by Gribov copies. A possible method-independent gauge
definition to resolve this problem is presented and afterwards used to study
the properties of gluons at any temperature. It is found that only
chromo-electric properties reflect the phase transition. From these the
gauge-invariant phase transition temperature is determined for SU(2) and SU(3)
Yang-Mills theory independently.Comment: 3 pages, 1 figure. Talk given at "The 5-th International Conference
on Quarks and Nuclear Physics", Beijing, China, and at "Quarks, Hadrons, and
the Phase Diagram of QCD", St. Goar, Germany, both September 2009. Submitted
to the QNP proceeding
Optical Line Width Broadening Mechanisms at the 10 kHz Level in Eu3+:Y2O3 Nanoparticles
We identify the physical mechanisms responsible for the optical homogeneous broadening in Eu3+:Y2O3 nanoparticles to determine whether rare-earth crystals can be miniaturized to volumes less than λ3 whilst preserving their appeal for quantum technology hardware. By studying how the homogeneous line width depends on temperature, applied magnetic field, and measurement time scale the dominant broadening interactions for various temperature ranges above 3 K were characterized. Below 3 K the homogeneous line width is dominated by an interaction not observed in bulk crystal studies. These measurements demonstrate that broadening due to size-dependent phonon interactions is not a significant contributor to the homogeneous line width, which contrasts previous studies in rare-earth ion nanocrystals. Importantly, the results provide strong evidence that for the 400 nm diameter nanoparticles under study the minimum line width achieved (45±1 kHz at 1.3 K) is not fundamentally limited. In addition, we highlight that the expected broadening caused by electric field fluctuations arising from surface charges is comparable to the observed broadening. Under the assumption that such Stark broadening is a significant contribution to the homogeneous line width, several strategies for reducing this line width to below 10 kHz are discussed. Furthermore, it is demonstrated that the Eu3+ hyperfine state lifetime is sufficiently long to preserve spectral features for timescales up to 1 s. These results allow integrated rare-earth ion quantum optics to be pursued at a sub-micron scale and hence, open up directions for greater scaling of rare-earth quantum technology
Juvenile polyposis of infancy in a child with deletion of BMPR1A and PTEN genes: Surgical approach
Juvenile polyposis of infancy is the most severe and life-threatening form of juvenile polyposis. This disease typically presents in the first two years of life with gastrointestinal bleeding, diarrhea, inanition, and exudative enteropathy. In very few reports concerning this entity, a large deletion in the long arm of chromosome 10 (10q23), encompassing the PTEN and BMPR1A genes, was found. The authors report a case of delayed diagnosis of juvenile polyposis of infancy at 6years of age. A 3.34Mb long de novo deletion was identified at 10q23.1q23.31, encompassing the PTEN and BMPR1A genes. The disease course was severe with diarrhea, abdominal pain, inanition, refractory anemia, rectal bleeding, hypoalbuminemia, and exudative enteropathy. A sub-total colectomy, combined with intraoperative endoscopic removal of ileal and rectal stump polyps, was required for palliative disease control
Identification of transitional disks in Chamaeleon with Herschel
Transitional disks are circumstellar disks with inner holes that in some
cases are produced by planets and/or substellar companions in these systems.
For this reason, these disks are extremely important for the study of planetary
system formation. The Herschel Space Observatory provides an unique opportunity
for studying the outer regions of protoplanetary disks. In this work we update
previous knowledge on the transitional disks in the Chamaeleon I and II regions
with data from the Herschel Gould Belt Survey. We propose a new method for
transitional disk classification based on the WISE 12 micron-PACS 70 micron
color, together with inspection of the Herschel images. We applied this method
to the population of Class II sources in the Chamaeleon region and studied the
spectral energy distributions of the transitional disks in the sample. We also
built the median spectral energy distribution of Class II objects in these
regions for comparison with transitional disks. The proposed method allows a
clear separation of the known transitional disks from the Class II sources. We
find 6 transitional disks, all previously known, and identify 5 objects
previously thought to be transitional as possibly non-transitional. We find
higher fluxes at the PACS wavelengths in the sample of transitional disks than
those of Class II objects. We show the Herschel 70 micron band to be an
efficient tool for transitional disk identification. The sensitivity and
spatial resolution of Herschel reveals a significant contamination level among
the previously identified transitional disk candidates for the two regions,
which calls for a revision of previous samples of transitional disks in other
regions. The systematic excess found at the PACS bands could be a result of the
mechanism that produces the transitional phase, or an indication of different
evolutionary paths for transitional disks and Class II sources.Comment: Accepted for publication in A&A: 11 March 2013 11 pages, 15 figure
Micromegas in a Bulk
In this paper we present a novel way to manufacture the bulk Micromegas
detector. A simple process based on the PCB (Printed Circuit Board) technology
is employed to produce the entire sensitive detector. Such fabrication process
could be extended to very large area detectors made by the industry. The low
cost fabrication together with the robustness of the electrode materials will
make it extremely attractive for several applications ranging from particle
physics and astrophysics to medicineComment: 6 pages, 4 figure
Existence of weak solutions for the generalized Navier-Stokes equations with damping
In this work we consider the generalized Navier-Stokes equations with the presence of a damping term in the momentum equation. The problem studied here derives from the set of equations which govern isothermal flows of incompressible and homogeneous non-Newtonian fluids. For the generalized Navier-Stokes problem with damping, we prove the existence of weak solutions by using regularization techniques, the theory of monotone operators and compactness arguments together with the local decomposition of the pressure and the Lipschitz-truncation method. The existence result proved here holds for any and any sigma > 1, where q is the exponent of the diffusion term and sigma is the exponent which characterizes the damping term.MCTES, Portugal [SFRH/BSAB/1058/2010]; FCT, Portugal [PTDC/MAT/110613/2010]info:eu-repo/semantics/publishedVersio
Herschel survey of brown dwarf disks in Rho Ophiuchi
Recent observations of the Rho Ophiuchi cluster with the Herschel Space
Observatory allow us to probe the spectral energy distribution (SED) of the
brown dwarf population in the far-IR, where the disk emission peaks. We
performed aperture photometry at 70, 100, and 160 micron, and constructed SEDs
for all previously known brown dwarfs detected. These were complemented with
ancillary photometry at shorter wavelengths. We compared the observed SEDs to a
grid of synthetic disks produced with the radiative transfer code MCFOST, and
used the relative figure of merit estimated from the Bayesian inference of each
disk parameter to analyse the structural properties. We detected 12 Class II
brown dwarfs with Herschel, which corresponds to one-third of all currently
known brown dwarf members of Rho Ophiuchi. We do not detect any of the known
Class III brown dwarfs. Comparison to models reveals that the disks are best
described by an inner radius between 0.01 and 0.07 AU, and a flared disk
geometry with a flaring index between 1.05 and 1.2. Furthermore, we can exclude
values of the disk scale-height lower than 10 AU (measured at a fiducial radius
of 100 AU). We combined the Herschel data with recent ALMA observations of the
brown dwarf GY92 204 (ISO-Oph 102), and by comparing its SED to the same grid
of disk models, we derived an inner disk radius of 0.035 AU, a scale height of
15 AU with a flaring index of beta~1.15, an exponent for dust settling of -1.5,
and a disk mass of 0.001 MSun. This corresponds to a disk-to-central object
mass ratio of ~1%. The structural parameters constrained by the extended SED
coverage (inner radius and flaring index) show a narrow distribution for the 11
young brown dwarfs detected in Rho Ophiuchi, suggesting that these objects
share the same disk evolution and, perhaps, formation.Comment: Accepted for publication in A&
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